The present invention relates generally to an electronic shutter, and more particularly to a non-polarizing electronic shutter for a still image capturing device.
Still image capturing devices are used to visually memorialize scenes, events, or items. Still image capturing devices, such as cameras, include a lens, a shutter, and either a photosensitive film or an electronic image sensor. In addition, most modern cameras include a processor and/or other control electronics that function to control shutter speed, aperture, flash, focus, etc.
In operation, the shutter is opened briefly to expose the film or the electronic image sensor and thereby form an image. The duration of the shutter opening is very critical and the quality of the captured image depends on a proper exposure time based on lighting, movement of the subject, focus distance, etc. Accurate and reliable shutter actuation is therefore the most important operation in a still image capturing device and must be accurately controlled in order to produce a satisfactory image.
A first prior art shutter approach is a mechanical shutter. The mechanical shutter has been widely used for a number of years and is generally in the form of an iris-type shutter. However, the prior art mechanical shutter has many drawbacks including weight, large size, susceptibility to dirt and wear, and the difficulty of precisely controlling shutter exposure times over a wide range of conditions. In addition, the typical iris-type mechanical shutter exposes the center of the image for a longer time than the edges of the image.
In some prior art cameras, the mechanical shutter is electronically activated by a motor or other electrical actuator. This may produce more accurate shutter control, but consumes a lot of electrical energy and still exposes the image unevenly.
One approach to eliminating these drawbacks has been to use an electronic shutter, such as a liquid crystal display (LCD) element. This gives a prior art camera an advantageous precise electronic control over exposure times. In addition, the LCD element may be switched to a light transparent mode over all regions of the LCD element at once, unlike a mechanical iris shutter. This produces an even exposure time over the entire image area. In addition, an electronic LCD shutter can be set to varying levels of opacity in order to reduce the brightness of very bright scenes.
However, the prior art electronic LCD shutter has several drawbacks. Because a LCD device polarizes the light that passes through it, prior art LCD shutters capture an image using polarized light. This may produce light irregularities if the light source used to capture the image is polarized, since only light polarized in a single plane passes through the shutter. In addition, the dual polarizing films used in prior art LCD shutters significantly reduce the amount of light that reaches the film or electronic imaging element.
Therefore, there remains a need in the art for improvements in still image capturing devices.
An electronic shutter apparatus for a still image capturing device is provided according to one embodiment of the invention. The apparatus comprises a beam splitter positioned in an incoming light beam path and splitting the incoming light beam into a first light beam and a second light beam. The apparatus further comprises first and second polarizing shutters respectively positioned in paths of the first and second light beams and capable of being electrically activated to transmit light and to respectively form first and second polarized light beams. A polarization orientation of light from the second polarizing shutter is in non-alignment with a polarization orientation of light from the first polarizing shutter. The apparatus further comprises a beam combiner receiving and combining the first and second polarized light beams to form a substantially non-polarized resultant light beam. The resultant light beam is focused onto an image sensor.
According to another embodiment of the invention, an electronic shutter apparatus for a still image capturing device is provided which comprises a beam splitter means for splitting the incoming light beam path into a first light beam and second light beam. The apparatus further comprises first and second polarizing shutters respectively positioned in paths of the first and second light beams and capable of being electrically activated to transmit light and to respectively form first and second polarized light beams. A polarization orientation of light from the second polarizing shutter is in non-alignment with a polarization orientation of light from the first polarizing shutter. The apparatus further comprises a beam combiner means for combining the first and second polarized light beams to form a substantially non-polarized resultant light beam. The apparatus further comprises two or more reflecting means for reflecting and directing the first and second light beams into the first and second polarizing shutters and for reflecting and directing the first and second polarized light beams into the beam combiner means. The apparatus further comprises a processor controlling the first and second polarizing shutters to selectively admit light to the image sensor of the still image capturing device.
According to yet another embodiment of the invention, a light shuttering method for a still image capturing device is provided, which comprises the steps of splitting an incoming light beam into a first light beam and a second light beam, providing a first polarizing shutter in the first light beam to produce a first polarized light beam, and providing a second polarizing shutter in the second light beam to produce a second polarized light beam. A polarization orientation of light from the second polarizing shutter is in non-alignment with a polarization orientation of light from the first polarizing shutter. The method further comprises the step of combining the first polarized light beam and the second polarized light beam to form a substantially non-polarized resultant light beam and providing the resultant light beam to an image sensor of the still image capturing device.